Double poloidal field coils

Abstract

A poloidal field coil assembly for use in a tokamak. The poloidal field coil assembly comprises inner and outer poloidal field coils and a controller. The inner poloidal field coil is configured for installation inside a toroidal field coil of the tokamak. The outer poloidal field coil is configured for installation outside the toroidal field coil. The controller is configured to cause current to be supplied to the inner and outer poloidal field coils such that the combined magnetic field produced by the inner and outer poloidal field coils has a null at the toroidal field coil.

The invention claimed is: 
     
       1. A method of operating a magnet assembly in a tokamak, the method comprising:
 providing a magnet assembly including:
 a poloidal field coil assembly having an inner poloidal field coil and an outer poloidal field coil, 
 a toroidal field coil including superconducting material, and 
 a controller; 
 
 installing the inner poloidal field coil inside the toroidal field coil; 
 installing the outer poloidal field coil outside the toroidal field coil; and 
 supplying, by the controller, current to the inner poloidal field coil and the outer poloidal field coil to create a combined magnetic field produced by the combination of the inner poloidal field coil and the outer poloidal field coil,
 wherein the combined magnetic field has a null at the toroidal field coil, 
 wherein the controller causes the null at a predetermined location on the toroidal field coil. 
 
 
     
     
       2. A method according to  claim 1 , wherein the toroidal field coil includes a joint, and further comprising supplying, by the controller, current to the inner poloidal field coil and the outer poloidal field coil such that the null is located at the joint. 
     
     
       3. A method according to  claim 1 , wherein the tokamak is a spherical tokamak. 
     
     
       4. A method according to  claim 1 , wherein one or more of the toroidal field coil, the inner poloidal field coil, and the outer poloidal field coil include a high temperature superconductor. 
     
     
       5. A magnet assembly for use in a tokamak, the magnet assembly comprising:
 a poloidal field coil assembly; 
 a toroidal field coil including superconducting material; 
 an inner poloidal field coil installed inside the toroidal field coil; 
 an outer poloidal field coil installed outside the toroidal field coil; and 
 a controller configured to cause current to be supplied to the inner and outer poloidal field coils to create a combined magnetic field produced by the inner and outer poloidal field coils,
 wherein the combined magnetic field has a null at the toroidal field coil, 
 wherein the controller is configured to cause the null at a predetermined location on the toroidal field coil. 
 
 
     
     
       6. A magnet assembly according to  claim 5 , wherein each poloidal field coil comprises a high temperature superconductor. 
     
     
       7. A magnet assembly according to  claim 5 , wherein the toroidal field coil comprises a joint, and wherein the inner and outer poloidal field coils are positioned such that the combined magnetic field produced by the inner and outer poloidal field coils has the null at the joint. 
     
     
       8. A tokamak comprising a toroidal plasma chamber and a magnet assembly according to  5 . 
     
     
       9. A tokamak according to  claim 8 , wherein the tokamak is a spherical tokamak.